The goal of this project is to understand the genetic and molecular basis of determination and positional information. I propose to analyze these phenomena in the imaginal discs of Drosophila, because a great deal is already known about disc development and they are an extremely convenient source of material. I propose to analyze determination by studying homoeotic mutations of the bithorax complex that cause segmental transformations in the thorax and abdomen of Drosophila. By the appropriate in vivo culture experiments I will determine what aspect of the determination system has been altered by various mutations. By the use of high resolution two-dimensional gel electrophoresis and the unique properties of tissue transformed by a mutation which I have previously studied I hope to identify the protein or proteins involved in metathoracic determination. The positional information system of imaginal discs appears to be the same in all discs, and indeed as part of this project I have demonstrated position specific interactions between fragments of the wing and haltere discs. As part of the project a study of regional biochemical differences in discs is being undertaken. The major effort here is utilizing two-dimensional gel electrophoresis. I have also begun to examine cellular and molecular events during pattern regulation.